Advice for hyperactive and anxious dog

I have a foster dog who is extremely hyperactive. She's actually fairly well behaved in comparison to other hyperactive dogs, but the thing that stumps me is when her anxious side comes through into the hyperactivity. She is not a nervous dog by any means, but she is anxious. If that makes sense... Nothing phases her. She'll greet any stranger and be oblivious to any thunderstorm. But her hyperactivity can turn into what I can only describe as anxiousness.

She's not a dog you can just let wear themselves out and call it a day. She will go and go and go, likely until she truly can't go anymore which is what scares me. It can be 90 something degrees outside, this pup just ran around like crazy with her foster brother, she's panting like no tomorrow and she still just can't hold still. She's absolutely exhausted and gasping with every pant but she refuses to stop moving. She walks around almost mindlessly, will even trip over herself or anything in her way. If I manage to get her to sit (or rarely lay) down she's up a few seconds later aimlessly walking around with no direction or intent. She is the poster child of doggie ADHD.

My question is, what's the explanation/root for this behavior and what's the best way to deal with it? It gets in the way of training because she is often reckless, even to the point of self harm. Even if I know she knows how she should behave when she's in that state of mind it's like the outer world is a blur to her.